Offset ablation profiles for treatment of irregular astigmatism

ABSTRACT

The invention provides near-term customized ablation capabilities for treatment of corneal irregularities by ablating laterally offset refractive therapy profiles. These treatment profiles may, when centered on the eye, be suitable for treatment of standard refractive errors such as myopia, hyperopia, and cylindrical astigmatism. By selectively offsetting one or more of these ablation profiles at selected points across the corneal surface, the laser system can reduce refractive errors resulting from corneal irregularities such as irregular astigmatism, corneal steepening in one quadrant, asymmetrical astigmatism, irregularities inadvertently produced by a prior refractive treatment (such as radial keratotomy incisions, a decentered ablation, or the like), granular dystrophy, diffuse, asymmetric warpage as a result of post-corneal transplants, bilateral keratoconus, penetrating keratoplasty, or the like.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present application is a continuation patent application ofand claims the benefit of priority from U.S. patent application Ser. No.09/287,322 filed Apr. 7, 1999, the full disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention generally relates to laser eye surgery, and inparticular, provides methods, devices, and systems for selectivelyablating corneal tissue to improve the vision of patients having cornealirregularities.

[0004] Laser eye surgery systems and methods are now used to correctdefects in vision using a technique known as ablativephotodecomposition. In general, these techniques selectively expose thecornea to laser radiation so as to selectively remove and resculpt thecornea and achieve a desired change in shape of the cornea to treat anoptical defect.

[0005] Laser eye surgery is now being used to treat a variety of visiondefects, including myopia (nearsightedness), hyperopia (farsightedness),and symmetrical cylindrical astigmatisms. To achieve these results,known laser eye surgery systems make use of a variety of mechanisms toselectively expose the corneal tissue to the ablative laser energy so asto change the optical characteristics of the eye uniformly throughoutthe optically used portion of the cornea. Often times, the desiredchange in shape is effected by selectively removing corneal tissueaccording to a spherical ablation profile (for example, for treatment ofmyopia and hyperopia). Cylindrical astigmatism is often treated byselectively removing corneal tissue according to a cylindrical profile,in which the cylinder extends laterally across the optical axis of theeye.

[0006] Many patients suffer from optical defects which are not easilytreated using known spherical or cylindrical ablation techniques. It hasbeen proposed to treat patients suffering from nonsymmetrical or othertypes of astigmatism by defining a custom ablation profile. Ophthalmicmeasurement techniques which may be capable of generating highlyaccurate topographic information on a particular cornea are now beingdeveloped. Unfortunately, integrating these topographic measurementstogether with new ablation algorithms may take years. In the meantime,patients having irregular corneal defects which significantly limittheir vision are in need of treatment today.

[0007] In light of the above, it would be desirable to provide improvedlaser eye surgery devices, systems, and methods. It would be beneficialif these improvements allowed the treatment of irregular cornealdefects, particularly if these benefits were available and safe for usein the near-term.

[0008] 2. Description of the Background Art

[0009] The following patents and patent applications may be relevant tothe present invention: U.S. Pat. No. 5,683,379, issued Nov. 4, 1997, for“Apparatus for Modifying the Surface of the Eye Through Large Beam LaserPolishing and Method of Controlling the Apparatus”; U.S. Pat. No.4,724,522, issued Feb. 9, 1988, for “Method and Apparatus forModification of Corneal Refractive Properties”; U.S. Pat. No. 5,098,426,issued Mar. 24, 1992, for “Method and Apparatus for Precision LaserSurgery”; U.S. Pat. No. 5,290,272, issued Mar. 1, 1994, for “Method forthe Joining of Ocular Tissues Using Laser Light”; U.S. Pat. No.5,314,422, issued May 24, 1994, for “Equipment for the Correction ofPresbyopia by Remodelling the Corneal Surface by Means ofPhoto-Ablation”; U.S. Pat. No. 5,391,165, issued Feb. 21, 1995, for“System for Scanning a Surgical Laser Beam”; U.S. Pat. No. 5,439,462,issued Aug. 8, 1995, for “Apparatus for Removing Cataractous Material”;U.S. Pat. No. 5,549,596, issued Aug. 27, 1996, for “Selective LaserTargeting of Pigmented Ocular Cells”; U.S. Pat. No. 5,549,597, issuedAug. 27, 1996, for “In Situ Astigmatism Axis Alignment”; U.S. Pat. No.5,556,395, issued Sep. 17, 1996, for “Method and System for LaserTreatment of Refractive Error Using an Offset Image of a RotatableMask”; U.S. Pat. No. 5,634,919, issued Jun. 3, 1997, for “Correction ofStrabismus by Laser-Sculpting of the Cornea”; U.S. Pat. No. 5,637,109,issued Jun. 10, 1997, for “Apparatus for Operation on a Cornea UsingLaser-Beam”; PCT International Application No. PCT/EP95/01287, filedApr. 7, 1995, for “Method and Apparatus for Providing Precise Locationof Points on the Eye”; European Patent Application No. 94303256.5, filedMay 5, 1994, for “Method and System for Laser Treatment of RefractiveErrors Using Offset Imaging”; and U.S. patent application Ser. No.09/274,499, filed Mar. 23, 1999, for “Multiple Beam Laser SculptingSystem and Method”. The full disclosure of these references is herebyincorporated by reference.

SUMMARY OF THE INVENTION

[0010] The present invention provides improved laser eye surgerydevices, systems, and methods. The invention provides near-termcustomized ablation capabilities for treatment of corneal irregularitiesby ablating standard refractive therapy profiles at a position which isoffset from the pupillary center. These treatment profiles may, whencentered on the eye, be suitable for treatment of standard refractiveerrors such as myopia, hyperopia, and symmetrical cylindricalastigmatism. By selectively offsetting one or more of these ablationprofiles at selected points across the corneal surface, the laser systemcan reduce refractive errors resulting from corneal irregularities suchas irregular astigmatism, corneal steepening in one quadrant,asymmetrical astigmatism, irregularities inadvertently produced by aprior refractive treatment (such as radial keratotomy incisions, adecentered ablation, asymmetric warpage as a result of cornealtransplants, penetrating keratoplasty, or the like), granular dystrophy,diffuse, bilateral keratoconus, or the like.

[0011] In a first aspect, the invention provides a method for treatingan eye of a patient. The eye has a cornea and a pupil, the pupil havinga center. The method comprises aligning a laser delivery system with thepupil of the eye. A treatment center on the cornea is designated so thatthe treatment center is offset laterally (in the X and/or Y direction)from the center of the pupil. A region of the cornea is ablated bydirecting laser energy according to a therapy profile centered at thetreatment center, which may be at some distance from the pupillarycenter.

[0012] The therapy may further comprise selecting the therapy profilefrom a library including a myopic treatment profile, a hyperopictreatment profile, and a cylindrical treatment profile. These treatmentprofiles may be scaled for both size and power, and still furthertherapy profiles may be included in the library. A more complete librarymay include myopic ablations which are spherical, cylindrical, and/orelliptical in shape; hyperopic ablations which are spherical,cylindrical, and/or provide smooth transition zones; and optionallyincluding therapeutic ablations such as phototherapeutic keratectomyslits and/or phototherapeutic keratectomy circles of variable sizes andhaving variable transition zones.

[0013] Corneal irregularities will often benefit from combinations oftwo or more therapy profiles centered at different treatment centers onthe cornea. By providing a variety of different treatment profiles whichcan be scaled and selectively offset from each other, often at leastpartially overlapping on the corneal surface, a wide variety ofcustomized contoured ablations may be effected without having togenerate individual customized ablation algorithms to effect the desiredoverall treatment profile.

[0014] The particular profile or profiles applied to a patient's eyewill often be identified or planned using a map of the cornea. Elevationmaps, such as those which might be produced using wavefront technologynow under development, are particularly beneficial for selecting,scaling, and offsetting the therapy profiles over the corneal surface tomitigate the corneal irregularity. Advantageously, it is not necessaryto (although it is possible to) link these developmental topographysystems to the ablation system to generate customized therapies.Instead, a system operator may select individual ablation size, shape,location, and power based on a topography map, so as to plan the totalcombined treatment, optionally simulating the effect of the proposedablation before it is implemented. In fact, while elevation map dataresults are preferred due to their accuracy and location, depth, andsize of irregular corneal features, tangential and/or axial maps may beused independently and advantageously combined to supply the desiredinformation.

[0015] In another aspect, the invention provides a system for treatingan eye of a patient. The eye has a cornea and pupil with a center. Thesystem comprises a laser producing a laser beam capable of ablating thecornea. Delivery optics are coupled to the laser. Alignment optics arealigned with the delivery optics for maintaining alignment between thelaser and the pupil of the eye. An input for designating at least onetreatment center is coupled to the delivery optics. The treatment centeris offset laterally from the center of the pupil while the pupil of theeye is aligned with the alignment optics.

[0016] In a standard symmetrical ablation, alignment optics are alignedwith the delivery optics so that the delivered laser beam is coincidentand concentric with the alignment reticle. The patient's pupil isgenerally aligned to the reticle of the alignment optics. If a treatmentis desired wherein the treatment beam is not to be centered on thepupil, the operator can specify how far and in what direction the beamis to be displaced from the alignment center. Typically, a controllerwill direct the optics to deflect the beam laterally so as to effect atreatment profile centered about the designated treatment center. Thetreatment profile will often be produced by directing numerousindividual laser pulses over varying overlapping regions of the cornea.The controller and delivery optics may make use of small spot scanningtechniques, large area ablation techniques with variable blocking of thelaser energy, and/or overlapping intermediate sized spots which arelaterally deflected using mirrors, lenses, or the like. The controllermay effect the treatment profiles by moving scanning mechanisms,selecting apertures, varying iris or slot sizes, often according to atreatment table or position calculation algorithm. Regardless, thecontroller will preferably have and/or make use of a tangible datastorage medium with a library of alternative refractive therapies whichmay be selected and/or scaled individually or in combinations. Thelibrary will typically include profiles suitable for treatment ofmyopia, hyperopia, and cylindrical astigmatism when centered on theoptical axis of the eye. By offsetting one or more of these therapies, awide variety of corneal irregularities may be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 schematically illustrates a custom ablation system whichapplies refractive therapy profiles at a location laterally offset froman optical axis of the eye.

[0018]FIGS. 2 and 3 schematically illustrate an optical train forselectively directing a laser beam onto the corneal tissue.

[0019]FIG. 4 is a function block diagram illustrating the control inscanning architecture of the customized ablation system of FIG. 1.

[0020]FIGS. 5 through 8 schematically illustrate the use of off-centerrefractive ablation profiles for treatment of corneal irregularities.

[0021]FIG. 9 is a flowchart illustrating steps for treatment of a corneairregularity using offset ablation profiles.

[0022]FIG. 10 illustrates therapy profiles and scale parameters includedwithin an exemplary library.

[0023]FIGS. 11A and B illustrate data entry screens for selecting,offsetting, scaling, and combining standard ablation profiles to treatcorneal irregularities.

[0024]FIGS. 12A through C schematically illustrate alternative maps forplanning a custom combined ablation.

[0025]FIG. 13 illustrates information displayed for planning andsimulating a combined ablation to verify the proposed combination ofablation profiles prior to treatment of the eye.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0026] Referring now to FIG. 1, a system 10 for treatment of cornealirregularities directs a laser beam 12 from a laser 14 to an eye Ehaving a cornea C. A pupil P has a center defining an optical axis A.

[0027] An optical train 16 variably directs laser beam 12 onto thesurface of cornea C according to a treatment profile. Rather thantreating cornea C with a profile centered about axis A, an operatordesignates a treatment center 18 which is offset laterally (oftendescribed as the X-Y plane) from the center of pupil P.

[0028] The operator designates treatment center 18 using an input 20coupled to controller 22, the input here schematically illustrated as ajoystick. The orientation of eye E is stabilized by the patient viewinga fixation target 24 through alignment optics 26. The operator willoften direct the ablation procedure while viewing eye E through amicroscope 28.

[0029] Referring now to FIG. 2, laser delivery optics 16 for directinglaser beam 12 at eye E will often include a number of mirrors 30, aswell as one or more integrators 32 which may even (or otherwise tailor)the energy distribution across the laser beam. Laser 14 will oftencomprise an excimer laser or a suitably frequency multiplied solid statelaser generating laser energy having a frequency suitable for cornealtissue ablation with minimal thermal damage to the underlying tissue.The laser system may include, but is not limited to, excimer lasers suchas argon-fluoride excimer lasers (producing laser energy with awavelength of about 193 nm), solid state lasers, including frequencymultiplied solid state lasers such as flash-lamp and diode pumped solidstate lasers. Exemplary solid state lasers include UV solid state lasers(approximately 193-215 nm) such as those disclosed in U.S. Pat. Nos.5,144,630 and 5,742,626, Borsuztky et al., “Tunable UV Radiation atShort Wavelengths (188-240 nm) Generated by Sum Frequency Mixing inLithium Borate”, Appl. Phys. 61:529-532 (1995), and the like. The laserenergy may comprise a beam formed as a series of discreet laser pulses.A variety of alternative lasers might also be used.

[0030] In the exemplary embodiment, a variable aperture 34 changes adiameter and/or slot width to profile laser beam 12, ideally includingboth a variable diameter iris and a variable width slot. A prism 36separates laser beam 12 into a plurality of beamlets, which maypartially overlap on eye E to smooth edges of the ablation or “crater”from each pulse of the laser beam. Referring now to FIGS. 2 and 3, anoffset module 38 includes motors 40 which vary an angular offset of anoffset lens 42, and which also change the radial orientation of theoffset. Hence, offset module 38 can selectively direct laser beam 12 ata desired lateral region of the cornea. A structure and method for usingoptical train 16 and offset module 38 are more fully described inco-pending U.S. patent application Ser. No. 08/968,380, entitled “Methodand System for Laser Treatment of Refractive Errors Using OffsetImaging” filed Nov. 12, 1997; U.S. patent application Ser. No.09/185,914, entitled “Method and System for Laser Treatment ofRefractive Errors Using Offset Imaging” filed Nov. 4, 1998; and U.S.patent application Ser. No. 09/274,499, entitled “Multiple Beam LaserSculpting System and Method”, filed Mar. 23, 1999, the full disclosuresof which are incorporated herein by reference.

[0031] Referring now to FIG. 4, elements of a VISX Star S2™ excimerlaser system, as commercially available from VISX, Incorporated of SantaClara, Calif., are schematically illustrated as modified for useaccording to the principles of the present invention. A computer controlsystem 22 enables precise control of laser system 10 to sculpt a surfaceshape specified in a laser treatment table 302. A controller 22, whichgenerally comprises a PC workstation, makes use of a computer programstored on a tangible media 304 to generate treatment table 302. Anembedded computer 308 within laser system 10 is in electroniccommunication with the PC workstation, and may thereby comprise aportion of the overall controller. Alternatively, a PC workstation maybe embedded in the laser system and function as both the embeddedcomputer and PC workstation for directing the ophthalmic surgery.

[0032] Embedded computer 308 is in electronic communication with aplurality of sensors 306 and a plurality of motor drivers 310. The motordrivers are coupled to the controller to vary the position andconfiguration of many of the optical components of the delivery optics16 according to treatment table 302. For example, first and secondscanning axis 320, 330 control the position of the offset lens to movethe beamlets over the surface of the cornea. Iris motor 340 controls thediameter of the overall beam, and in some cases, the length of lighttransmitted through a variable width slot. Similarly slot width driver350 controls the width of the variable slot. Slot angle driver 360controls rotation of the slot about its axis. Beam angle driver 370controls rotation of the beam, while laser 14 is pulsed to generate thelaser beam 12 after the various optical elements have been positioned tocreate a desired crater on eye E. Treatment table 302 may comprise alisting of all of the desired craters to be combined so as to effect atreatment therapy.

[0033] For customizing ablations to treat irregular corneas, controller22 will preferably include library 44 having a number of differentphotorefractive and/or phototherapeutic ablation profiles. Theseablation profiles will often be used for treatment of spherical and/orcylindrical refractive errors of the eye by coaxially locating treatmentcenter 18 at the center of pupil P. To treat irregular corneas, thesesame ablation profiles may be directed to laterally offset treatmentcenter 18 using input device 20. Conveniently, the controller can modifythe treatment table to offset the ablation profile by adjusting eachablation coordinate with the desired offset.

[0034] While the input device 20 is here schematically illustrated as ajoystick, it should be understood that a variety of input mechanisms maybe used. Suitable offset input mechanisms may include trackballs, touchscreens, or a wide variety of alternative pointing devices. Stillfurther alternative input mechanisms include keypads, data transmissionmechanisms such as an ethernet, intranet, internet, a modem, or thelike. These or other input mechanisms may be used to identify an offsettreatment center 18 which is offset laterally from the center of thepupil of the eye.

[0035] The use of standard ablation profiles to treat an irregularcornea can be understood with reference to FIGS. 5 through 8. Cornea Cin FIG. 6A features a protruding irregularity 46 of corneal tissue whichis offset laterally from the optical axis A. To treat this condition, aseries of laser pulses (schematically illustrated as pulses 12 a-d) ofgradually varying size are directed over a treatment region 48 which iscentered at offset treatment center 18. Such gradually varying diameterpulse patterns could be applied coaxially with the optical axis toflatten a central portion of the cornea and treat myopia. However, byoffsetting this same treatment profile laterally, protruding cornealtissue 46 may be ablated so as to resculpt the cornea to a morespherical shape, as illustrated in FIG. 6.

[0036] Alternative standard photorefractive therapies may also beapplied, as illustrated in FIG. 7. Cornea C here initially has a flatregion 50 having insufficient curvature. A hyperopia ablation profile52, which is most often used to increase the curvature of the centralcornea, is here offset laterally so as to be centered at offset center18 so as to increase the curvature of the corneal surface about flatregion 50.

[0037] Treatment of a previously decentered ablation is schematicallyillustrated in FIG. 8 using first a hyperopia ablation profile 52centered at offset treatment center 18 a, followed by a myopia ablationprofile 54 center at another offset treatment center 18 b so as todecrease the irregularity of the cornea throughout an optically usedregion 56. It should be understood that the examples illustrated inFIGS. 6A through 8 are schematic, that the offset treatment center maybe offset in both X and Y directions, and that the multiple treatmentcenters will often be radially offset from each other. Additionally, itshould be understood that the refractive treatment profiles will oftenbe scaled in size and power. Algorithms and techniques for generatingthe therapeutic ablation profiles by combining individual ablation pulsecraters are described in the patent literature listed hereinabove.

[0038] A flow chart 60 illustrating the individual steps for developinga custom ablation strategy is illustrated in FIG. 9. Preferably, a mapof the cornea will be prepared 62 using any of a wide variety ofcommercially available ophthalmic measurement techniques. Particularlyadvantageous topography measurements may be available using wavefronttechnology now being developed. As described hereinbelow, corneal mapsbased on the axial curvature or tangential curvature of the cornea mayalso be used independently, and/or these maps may be combined to backcalculate micron elevation data.

[0039] Based on the corneal map 62, a standard ablation profile isselected 64 with a proposed scale and offset 66. Where only a singleablation profile may be sufficient, the proposed ablation may then besimulated 68, with the resulting corneal characteristics presented toverify the proposed ablation parameters. In many cases, one or moreadditional ablation profiles may be added 70, or where appropriate,deleted from a previous ablation plan before the total ablationprocedure is simulated. If the ablation simulation 68 indicates furtherrefinement in the ablation plan would be beneficial, the plan may berevised by adding and/or subtracting ablation profiles, varying theoffset and scale of individual ablation profiles, or the like. If nofurther revision 72 is desired, the combined profile ablation plan maybe implemented to ablate the cornea 74.

[0040] An exemplary library of myopic, hyperopic, and therapeuticablation profiles is listed in FIG. 10. The standard ablation profilesmay be scaled in both dimensions and power, with the maximum and minimumscaling parameters being as listed. In general, photorefractive profilesrefer to both myopic profiles (or surfaces) and hyperopic profiles (orsurfaces) as listed, while therapeutic ablation profiles refer to thecorresponding shapes listed below the “therapeutic surface” heading.

[0041] The exemplary data input screens for selection of ablationprofiles, designating offsets and scales, and adding or subtractingprofiles are illustrated in FIGS. 11A and 11B. As illustrated in FIG.11A, a plurality of ablations may be entered for sequential and/orsimultaneous ablation with individually designated offsets and scaling.Entry of the parameters for a particular ablation profile such as theoffsets 80, size 82, and power 84 may be performed using a standardWindows™-type data entry system including a mouse or other pointingdevice and/or a keyboard.

[0042] Referring now to FIGS. 12A through C, elevation maps areparticularly advantageous for generating the desired ablation plan, asthey accurately indicate shape, location, depth, and size or irregularcorneal features, as illustrated in FIG. 12A. While axial curvature maps(as illustrated in FIG. 12B) provide good power values, they can be lessaccurate regarding the location and size of irregularities. Tangentialmaps such as that illustrated in FIG. 12C provide good location and sizeinformation, but may be less accurate regarding specific power values.Advantageously, axial and tangential maps can be combined so as to “backcalculate” elevation data, thereby significantly facilitating theplanning of a custom ablation profile.

[0043] Advantageously, a proposed ablation plan may be entered into thecomputer based on a visual review of the corneal map. The plan may betailored to treat asymmetrical astigmatism, inferior corneal steepening,corneal dystrophy, decentered ablations, errors inadvertently induced byprior refractive procedures, or a wide variety of other cornealirregularities. Proposed treatments may be generated to generallyimproved uncorrected visual acuity and/or optimize best corrected visualacuity for a particular patient. More generally, the tailored plan mayenhance the overall quality of vision and reduce visual aberrationscaused by irregularities.

[0044] Advantageously, it is not necessary to link a topography systemdirectly to an ablation system or ablation algorithm for generation of atreatment plan. Individual ablation profile settings and combinationsmay be controlled by the system operator, thereby providing near-termcapabilities for patient's suffering from these visual defects.Alternatively, it may be advantageous to eventually link the topographyinformation directly to the ablation profile planning computer. Hence,the selection, offset, and scaling of the ablation profiles may beperformed either manually and/or automatically. Regardless, the cornealmap and specific ablation mechanism may employ a variety of differentstructures within the scope of the present invention.

[0045] Referring now to FIG. 13, after (or optionally during) selectionand scaling of the individual ablation profiles based on a corneal map90, the computer may mathematically simulate the total ablation todetermine a change in the corneal map 92 and a resulting simulatedablated cornea 94, before actually removing corneal tissue. This allowsthe physician or other system operator to compare before and after mapsof the cornea so as to visualize the results, and to investigate avariety of alternative treatment plans prior to the actual ablation.

[0046] While the exemplary embodiment has been described in some detail,by way of example and for clarity of understanding, a variety ofadaptations, changes, and modifications will be obvious to those ofskill in the art. Hence, the scope of the present invention is limitedsolely by the appended claims.

What is claimed is:
 1. A method for treating an eye of a patient, theeye having a cornea and a pupil, the pupil having a center, the methodcomprising: aligning a laser delivery system with the pupil of the eye;designating a treatment center on the cornea, the treatment center beingoffset laterally from the center of the pupil; and ablating a region ofthe cornea by directing laser energy from the aligned laser deliverysystem according to a therapy profile centered at the treatment center,wherein the ablating step mitigates a refractive error produced by aprior treatment to the eye.
 2. The method of claim 1 , wherein the priortreatment comprises a prior ablation, and wherein the prior ablation wasoffset laterally from the center of the pupil.
 3. A system for treatingan eye of a patient, the eye having a cornea and a pupil, the pupilhaving a center, the system comprising: a laser producing a laser beamcapable of ablating the cornea; delivery optics coupled to the laser;alignment optics aligned with the delivery optics for maintainingalignment between the laser and the pupil of the eye; and an input fordesignating at least one treatment center coupled to the deliveryoptics, the treatment center offset laterally from the center of thepupil when the pupil of the eye is aligned with the alignment optics. 4.The system of claim 3 , further comprising a controller coupled to thedelivery optics, the controller directing the optics to deflect the beamlaterally so as to effect a treatment profile centered about thedesignated treatment center.
 5. The system of claim 3 , wherein thecontroller comprises a library of alternative refractive therapies, thealternative therapies individually selectable for ablating the corneaabout the designated treatment center, the library including a myopictreatment profile, a hyperopic treatment profile, and a cylindricalastigmatism treatment profile.
 6. The system of claim 3 , furthercomprising: a controller, the controller effecting a refractivecorrection of the eye by selectively directing the laser with thedelivery optics, the refractive correction comprising a regularrefractive correction when centered at the center of the pupil, thecontroller centering the refractive correction at the treatment centerso as to mitigate an irregular refractive error of the eye.